This invention relates to transducer mounting structures, and particularly to such structures adapting a transducer to controlled positioning use where there is relative motion with respect to a record surface.
Generally, in the recording and reproducing art, and particularly in the magnetic head recording and reproducing art, there has been difficulty in keeping the transducer (head) upon a predetermined linear or curvilinear path, such as a track that has been recorded in an irregular path, or that has been correctly recorded but subsequently distorted. Such difficulty occurs in the magnetic disc and magnetic drum art with respect to scanned paths that move in spirals or helices, or in circles eccentric to the center of rotation. However, extreme difficulty in tracking is present in the helical tape recording art with respect to recorded tracks that have been distorted, as by temperature or humidity-induced dimensional changes in the tape, or by faulty tensioning mechanisms in the tape transport. Additionally, in certain magnetic record medium applications it is desirable to control the recording path, e.g., to alter the direction of the path from its normal direction. In such applications, tracking is also important and difficult.
In the art, controlled transducer-to-medium positioning is accomplished by changing the relative head-to-medium speed or by adjusting the relative head-to-medium position. Examples of techniques in which the position and/or velocity of the record medium is controlled while being transported past the transducer are described in U.S. Pat. Nos. 3,663,736; 3,748,408 and 3,838,453. In some of these medium transport control positioning techniques, data reproduced from the record medium by a transducer whose tracking is to be controlled is monitored to provide a control signal for adjusting the transport of the record medium to maintain proper tracking by the transducer ('763 Patent). Others of these medium transport control positioning techniques utilize control track information separately recorded from the data to obtain control signals for adjusting tension of the record medium to maintain proper tracking by the transducer ('408 Patent). Still others of these medium transport control positioning techniques control both the speed of record medium transport and the position of the transported record medium relative to the transducer to maintain proper tracking by the transducer ('453 Patent). Changing the speed of transport of the record medium has the undesirable tendency of altering the time base of data reproduced from tracks recorded in the direction of the transport of the record medium. Furthermore, techniques which rely upon the control of the transport of the record medium to maintain proper tracking by the transducer are not suitable for precise control of the transducer position relative to paths along the record medium, particularly where large displacements (0.05 cm.) of transducer/record medium position may be required at high rates (200 deflection cycles per second) to maintain proper tracking by the transducer.
Positionable transducer mounting techniques also are employed to provide controlled tracking. For example, U.S. Pat. Nos. 3,126,535; 3,246,307 and 3,292,168 describe transducer positioners of the kind in which a transducer is carried at the end of a rigid arm ('307 and '535 Patents) or by other inflexible support ('168 Patent) that is moved back and forth by an actuator mechanism to position the transducer with respect to a selected path before transferring information to or from the scanned path. Such partitioners are satisfactory if the predictable path is followed with sufficient precision to obviate further positioning of the pre-positioned transducer. Many magnetic disc, drum and tape record/reproduce machines are able to position and transport their magnetic record media and transducers so that the tracks of recorded information follow such predictable paths. However, transducer positioners of the kind described in the aforementioned U.S. Patents are not suitable where very precise control of the transducer position is desired at all times, such as for transducers of rotary scan magnetic record/reproduce machines.
Energy transformers, such as piezoelectric transducers, have been used in various applications requiring controlled positioning of apparatus, including magnetic transducers (U.S. Pat. No. 3,526,726). A survey of piezoelectric transducers and their applications is presented in the article "Piezoelectric Ceramic Transducers" by Charles Edmiston, published in Electronic Design, 18 Sept. 1974, pages 78-82. Such transducers are especially attractive for use as low force, large displacement positioners. In the '726 Patent, piezoelectric transducer assemblies are described for reducing transducer displacement errors by positioning a normally stationary magnetic transducer in any one or more of three directions relative to longitudinal tracks along a longitudinally transported magnetic tape. Each piezoelectric transducer of the assembly is mounted as a simple beam that is bowed to adjust the position of the magnetic transducer suspended therefrom. Because the ends of each piezoelectric transducer of the described assemblies must be movably mounted to permit the piezoelectric transducer to be bowed, extraneous forces encountered by the assemblies can result in erroneous magnetic transducer displacements. Furthermore, the piezoelectric transducer assemblies described in the '726 Patent are not suitable for use in magnetic record/reproduce machines which employ magnetic transducers that are moved or are in motion during record and reproduce operations, especially in machines such as helical scan machines that employ low mass magnetic transducers which are subjected to high "g" forces during such operations.
Accordingly, it is an object of the present invention to provide an improved mounting for adapting a magnetic transducer for controlled positioning use.